During the past year we made significant progress in two areas: 1) continued development of a gene therapy for intravascular thrombosis, and 2) the development of a technique to introduce genetic material directly into the vascular wall, opening a potential means for the treatment of restenosis after angioplasty. In previous work we demonstrated that overexpression of tissue plasminogen activator (t-PA) from endothelial cells resulted in enhanced endothelial cell fibrinolytic activity. Major obstacles in the application of this technique to the treatment of intravascular thrombosis in humans included the presence of plasminogen activator inhibitor-1 (PAI-l)-mediated inhibition of t-PA, and the absence of an appropriate animal model in which to test the effect of t-PA gene transfer on thrombosis in vivo. We are now working with plasminogen activators which are resistant to PAI inhibition. Furthermore, in collaboration with Dr. Harker in Atlanta we are using an in vivo baboon model of intravascular thrombosis. To initiate the development of a genetic therapy for restenosis after angioplasty, we used a perforated balloon catheter to inject retroviral vectors into the rabbit arterial wall. A very low level of gene transfer was demonstrated. Future experiments will be directed at increasing the efficiency of this in vivo gene transfer system.